1. Field of the Invention
This invention relates to data processing systems. More particularly, this invention relates to data processing systems using table lookup instructions in which an index register holds a plurality of index values which are used to reference selected data elements within a table of data elements.
2. Description of the Prior Art
It is known to provide data processing systems supporting table lookup instructions. Such table lookup instructions are useful in a variety of different processing operations and are particularly well suited to systems in which a large volume of signal data, such as image or audio data, is to be processed. The table lookup instruction allows multiple data elements to be selected from a table in response to a single instruction. More particularly, an index register holding multiple index values may be referenced to determine which table entries within the table should be selected for further use.
Within a system having a load/store architecture in which data manipulations are only performed upon data value once they are stored within registers, the table of data to be accessed can be held within the data processing registers in order that high speed access may be made to it. However, the number of registers that can be devoted to storing a table is relatively low since the register resources of a system are usually in demand for holding and manipulating other data values and for other purposes. Thus, whilst it may be possible to calculate index values capable of accessing a large table, the table size is constrained by other factors and accordingly the usefulness of the table lookup instructions is reduced.